Trying to Have a Baby? Knowing How You Really Get Pregnant Can Help

Understanding how your reproductive cycle works will give you a head start on getting that little one on board sooner.

Trinette Reed/Stocksy

You may not have really thought about how a baby's made since, well, you got "the talk" from your parents or took that sex ed class in middle school. But now that you're trying to conceive, it's helpful to get a refresher course on the birds and bees. Learning about conception — and all the biology that goes into how two tiny cells, one from you and one from your partner, beat the odds to form a perfect union — is not only fascinating, but also practical. It will give you an understanding of how reproduction works — and how to get the good news you're expecting sooner.

What Is Ovulation?

You can debate all you want which comes first, the chicken or the egg. But when it comes to making a baby, there's no question: The egg comes first. Women are born with a lifetime supply of eggs (also called ova) — about 1 to 2 million of them, in fact. By the time you reach puberty — and start tapping into those eggs through ovulation — that number has gone down. But your ovaries still house about 300,000 to 500,000 of them. Even by the age of 37, most women continue to stockpile approximately 25,000 eggs.

Ovulation takes place when a single one of those thousands of eggs matures. The left and right ovaries typically alternate in sending out the next egg, which will then be taken into the fallopian tube by the petal-like fingers of the fimbriae.

Ovulation typically occurs halfway through a woman's menstrual cycle — and knowing when it takes place is of utmost importance to planning a pregnancy. Why? As the egg is hanging out in the fallopian tube, it's looking to meet its match — a single sperm — so fertilization might take place. But if there's no sperm around to greet the egg or if the sperm misses its mark and fertilization doesn't take place, the egg stops becoming viable within 12 to 24 hours.

That doesn't sound like much of an opening for conception — and it's not. But there's a little wiggle room thanks to the sperm. Assuming they've made their way into the fallopian tube after sex and ejaculation, they're able to live for a lot longer than an egg is willing to wait around. Sperm can survive in the female body for several days. This means that if you've had sex a few days before ovulation, there may still be plenty of sperm around to fertilize the egg.

Of course, having sex with your partner on the day you ovulate would be the best way to help the egg connect with a sperm. But knowing how to track your ovulation is tricky. The first day of your period is considered the first day of your menstrual cycle. A woman's typical menstrual cycle lasts an average of 28 days. If ovulation usually occurs halfway through the cycle, then peak fertility should happen at roughly 14 days after the start of your last period. However, there's a wide range of what's considered normal when it comes to your menstrual cycle; it can last the standard 28 days or anywhere from 21 to 35 days. To make matters more complicated, it may also vary slightly from month to month.

So while you may be eager to make baby magic happen — and there's always a chance it really can happen literally overnight — realistically the odds are that it will take a little longer. Even many healthy, fully fertile couples take six months or longer of actively trying to become pregnant.

What Is Fertilization?

You probably already have a pretty good idea of the role sex plays in making a baby. A man's testicles each produce about four million new sperm every hour (yes, every hour). Up to 200 million sperm will make their way into the vagina during ejaculation. That's the fun part (at least for you and your partner). But so much lies ahead for the sperm.

Semen, which is actually a nourishing mixture of complex sugars, protein and trace vitamins and minerals, feeds and fuels those sperm — and they need all the help they can get to make it from point A (your vagina) to point B (your egg waiting in the fallopian tube).

Their first challenge is the vagina itself. With its high levels of sperm-unfriendly acid, most sperm won't make it through the vagina. But if they do — and the best of the bunch are most equipped to do so — they'll be in the more welcoming cervical canal. There they'll be floating in cervical mucus and transforming from sluggish waders to tail-thrashing swimmers capable of making the seven-inch stretch that remains to the egg.

But the remaining sperm aren't anywhere near the finish line yet. First, they have to get their timing right. Arrive too early, and they risk losing viability before the egg shows up. Arrive too late, and they risk the egg no longer being viable and missing their shot. Also, they have to get their directions right. An egg is usually only present in one of your two fallopian tubes in any given month. Pick the wrong tube, and they'll be stood up at the end of their race.

Even the sperm that do reach the egg still have their work cut out for them. Once one finally succeeds in penetrating it, the egg triggers a barrier. This keeps out other sperm while the lucky one burrows into the center, where it will release its half of the genetic contribution to your baby. The egg is now officially fertilized.

Within a matter of hours, the fertilized egg (called a zygote) divides — and continues to do so again and again as it floats down the fallopian tube toward the uterus. By the time the cluster of cells (now called a blastocyst) reaches your uterus, about five days have passed and the blastocyst now comprises some 100 cells.

When Will Your Body Let You Know You're Pregnant?

When the blastocyst reaches your uterus, it's finally home — at least for the next eight and a half months. Once snug and secure in the uterine lining, the blastocyst's cells will split up. Half will become the placenta (the amazing lifeline that delivers nutrients to the fetus and carries away waste) and the other half (now called the embryo) will become your baby.

From the What to Expect editorial team and Heidi Murkoff, author of What to Expect Before You’re Expecting. Health information on this site is based on peer-reviewed medical journals and highly respected health organizations and institutions including ACOG (American College of Obstetricians and Gynecologists), CDC (Centers for Disease Control and Prevention) and AAP (American Academy of Pediatrics), as well as the What to Expect books by Heidi Murkoff.

The material on this website is provided for educational purposes only and is not to be used for medical advice, diagnosis or treatment, or in place of therapy or medical care. Use of this site is subject to our terms of use and privacy policy.